This application is for a Mentored Research Scientist Development Award (K01). The candidate, Tanja V.E. Kral, Ph.D., has a programmatic interest in studying behavioral traits associated with childhood obesity. The proposed research will be conducted within the broader context of a comprehensive training program which will be facilitated by an expert team of mentors. Dr. Kral's specific training goals are to receive training in 1) the conduct of experimental studies of eating behavior in children, 2) behavior genetics, 3) assessment of child body composition using dual energy x-ray absorptiometry (DEXA) and anthropometry, and 4) child development and biostatistics. Leading research institutes, in and out of the home institution, will serve as training sites for the candidate. We propose a discordant sibling design to compare putative obesity-promoting eating traits among siblings, 5-10 years, who are raised in the same household, but are discordant for weight status (non- overweight: BMI less or equal 75th percentile; at-risk for overweight/overweight: BMI greater or equal 85th percentile). Forty pairs of same-sex siblings (boys and girls) will be recruited from the greater Philadelphia area to participate in a 4-week study during which their eating behaviors will be assessed experimentally and under free-living conditions. The study tests the hypotheses that at-risk for overweight/overweight, compared to non-overweight, children exhibit 1) a weaker ability to compensate for energy, 2) a greater vulnerability towards eating in the absence of hunger, and 3) habitual intake patterns that favor increased dietary energy density (kcal/g), increased %energy derived from fat and caloric beverages, and fewer eating episodes. The use of a behavior genetic design to study eating phenotypes among siblings is a unique approach to elucidate shared and non-shared environmental influences that can contribute to variations in weight status during childhood. The proposed research has the potential to elucidate mechanisms by which environmental and genetic factors interact to promote increased energy intake among children. Together, the training and research plan will provide 5 years of critical mentored support to the candidate. The acquired skills and data will build the basis for the commencement of an independent R01 supported research program.